linux-kernel - Re: [PATCH 02/10] x86, asm: use bool for bitops and other assembly outputs

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Date:	Wed, 8 Jun 2016 10:33:40 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH 02/10] x86, asm: use bool for bitops and other assembly
 outputs


* Ingo Molnar <mingo@...nel.org> wrote:

> 
> * Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Tue, Jun 07, 2016 at 04:31:01PM -0700, H. Peter Anvin wrote:
> > > From: "H. Peter Anvin" <hpa@...or.com>
> > > 
> > > The gcc people have confirmed that using "bool" when combined with
> > > inline assembly always is treated as a byte-sized operand that can be
> > > assumed to be 0 or 1, which is exactly what the SET instruction
> > > emits.  Change the output types and intermediate variables of as many
> > > operations as practical to "bool".
> > > 
> > > Signed-off-by: H. Peter Anvin <hpa@...or.com>
> > > ---
> > >  arch/x86/boot/bitops.h             |  8 +++++---
> > >  arch/x86/boot/boot.h               |  8 ++++----
> > >  arch/x86/boot/string.c             |  2 +-
> > >  arch/x86/include/asm/apm.h         |  6 +++---
> > >  arch/x86/include/asm/archrandom.h  | 16 ++++++++--------
> > >  arch/x86/include/asm/atomic.h      |  8 ++++----
> > >  arch/x86/include/asm/atomic64_64.h | 10 +++++-----
> > >  arch/x86/include/asm/bitops.h      | 28 ++++++++++++++--------------
> > >  arch/x86/include/asm/local.h       |  8 ++++----
> > >  arch/x86/include/asm/percpu.h      |  8 ++++----
> > >  arch/x86/include/asm/rmwcc.h       |  4 ++--
> > >  arch/x86/include/asm/rwsem.h       | 17 +++++++++--------
> > >  include/linux/random.h             | 12 ++++++------
> > >  13 files changed, 69 insertions(+), 66 deletions(-)
> > 
> > So the only concern I have with this is that the x86 function signatures
> > are now different from the other architectures.
> > 
> > Not sure how much if anything that matters..
> 
> It does matter:
> 
>  In file included from arch/x86/kernel/cpu/common.c:21:0:
>  ./arch/x86/include/asm/archrandom.h:95:20: error: redefinition of ‘arch_get_random_long’
>  static inline bool arch_get_random_long(unsigned long *v)
>  In file included from ./arch/x86/include/asm/stackprotector.h:43:0,
>  include/linux/random.h:98:20: note: previous definition of ‘arch_get_random_long’ was here

Note that this particular build error was introduced by b0bdba9825fe, a later 
patch in this series - but in generaly I'm uneasy about allowing function 
signatures diverge between architectures.

Thanks,

	Ingo